Spark plug service unit



FIG. 1 is a top right front perspective view of a spark plug service unit showing our new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a left side elevational view thereof; and

FIG. 6 is a right side elevational view thereof. 

The ornamental design for a spark plug service unit, substantially as shown. 